The Doppler effect is defined as a noticeable change in the frequency of sound, light or water waves as the source and the observer move.(noun)
An example of the Doppler effect is that the frequency of the sound increases as the source moves closer to the observer.
See Doppler effect in Webster's New World College Dictionary
Origin: after C. Doppler (1803-53), Austrian mathematician and physicist
See Doppler effect in American Heritage Dictionary 4
Origin: After Christian Johann Doppler.
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